Cosmology

Heavy right-handed neutrinos are highly motivated due to their connection with the origin of neutrino masses via the seesaw mechanism. If the right-handed neutrino Majorana mass is at or below the weak scale, direct experimental discovery of these states is possible in laboratory experiments. However, there is no a priori basis to expect right-handed neutrinos to be so light since the Majorana mass is a technically natural parameter and could comfortably reside at any scale, including at scales far above the weak scale. Here we explore the possibility that the right-handed neutrino Majorana mass originates from electroweak symmetry breaking. Working within an effective theory with two Higgs doublets, nonzero lepton number is assigned to the bilinear operator built from the two Higgs fields, which is then coupled to the right-handed neutrino mass operator. In tandem with the neutrino Yukawa coupling, following electroweak symmetry breaking a seesaw mechanism operates, generating the light SM neutrino masses along with right-handed neutrinos with masses below the electroweak scale. This scenario leads to novel phenomenology in the Higgs sector, which may be probed at the LHC and at future colliders. There are also interesting prospects for neutrinoless double beta decay and lepton flavor violation. We also explore some theoretical aspects of the scenario, including the technical naturalness of the effective field theory and ultraviolet completions of the right-handed neutrino Majorana mass.

The Dark Energy Spectroscopic Instrument (DESI) is the first of a new generation of Dark Energy experiments and probes evolution in the universe using galaxy clustering. Within the galaxy clustering signal, the projected location of the Baryon Acoustic Oscillations (BAO) acts as a standard ruler to map cosmic evolution. I will present the latest BAO results from the DESI Data Release 2 (DR2) sample, which contains 3 years of data, and their impact on our understanding of dark energy and neutrino masses. Finally, I will consider how the amplitude of the BAO signal can help us measure the Hubble constant, potentially helping to solve the Hubble tension.

The existence of a population of massive quiescent galaxies with little to no star formation poses a challenge to our understanding of galaxy evolution. The physical process that quenched the star formation in these galaxies is debated, but the most popular possibility is that feedback from supermassive black holes lifts or heats the gas that would otherwise be used to form stars. In this paper, we evaluate this idea in two ways. First, we compare the cumulative growth in the cosmic inventory of the total stellar mass in quiescent galaxies to the corresponding growth in the amount of kinetic energy carried by radio jets. We find that these two inventories are remarkably well-synchronized, with about 50% of the total amounts being created in the epoch from z ≈ 1 to 2. We also show that these agree extremely well with the corresponding growth in the cumulative number of major mergers that result in massive (>10^11 M_ ʘ) galaxies. We therefore argue that major mergers trigger the radio jets and also transform the galaxies from disks to spheroids. Second, we evaluate the total amount of kinetic energy delivered by jets and compare it to the baryonic binding energy of the galaxies. We find the jet kinetic energy is more than sufficient to quench star formation, and the quenching process should be more effective in more massive galaxies. We show that these results are quantitatively consistent with recent measurements of the Sunyaev–Zel'dovich effect seen in massive galaxies at z ≈ 1.

Fast radio bursts (FRBs) are dispersed and scattered by plasma density fluctuations along the line-of-sight, making them sensitive probes of diffuse ionized gas across interstellar, circumgalactic, and intergalactic media. In this talk I will discuss how FRB propagation effects are unveiling cosmic plasmas at extremely small (sub-au) spatial scales in both interstellar and circumgalactic media, and how they may be used in tandem with quasars to constrain the turbulent dynamics of ionized gas in these environments.

The intergalactic medium gas is usually believed to simply trace the cosmic web structures traced by dark matter, but AGN feedback (especially jets) will probably modify this simple picture especially the IGM and CGM baryon budgets. I will talk primarily about the combining spectroscopic galaxy surveys with FRBs to probe the IGM and CGM balance, which is being implemented in the FLIMFLAM survey. I will highlight the role of Subaru PFS, the world's most powerful multiobject spectrograph, in efficiently mapping the cosmic web out to high redshift, and new applications of the field level inference technique towards this problem.

The cosmic web in the distant universe is generally mapped by observing the positions of galaxies. Recently a new perspective has been gained by mapping the diffuse gas in the intergalactic medium (IGM). The Lyman-Alpha Tomography IMACS Survey (LATIS) has now produced 3D maps of the IGM at redshift z~2.5, covering a volume of about 10^7 Mpc^3. I will present the LATIS maps and discuss how they inform our understanding of the interplay between early galaxies and their large-scale environments.

Remarkable parallels exist between observations of diffuse baryons and their connections to galaxies in the high redshift universe compared to z~0 ... in spite of apparently vast differences between the properties of the galaxies themselves and the nature and intensity of the feedback processes operating within them. I will attempt to draw connections between "contemporaneous" observations of galaxy-scale feedback in the adolescent universe with observable signatures "today", and attempt to distinguish between evolutionary sequences and possible coincidences that need further investigation.